1. Field of the Invention
The present invention relates to fuel supply apparatus for a direct injection type gasoline engine, for injecting high-pressure fuel directly into each cylindrical combustion chamber of the engine.
2. Description of Related Art
Recently, to improve economical fuel consumption and engine output power, a direct injection type gasoline engine has been developed in which fuel is injected directly into each cylindrical combustion chamber. In such a direct injection type gasoline engine, to facilitate atomization of fuel (gasoline) to be injected directly into each combustion chamber, the pressure of fuel supplied to fuel injection valves (fuel pressure) is increased to be high. Preferably, the fuel pressure should be increased to a high level promptly. Further, when fuel pressure varies during operation of the engine, the amount of injected fuel varies, and emission or driveability deteriorates. Therefore, it is preferable that fuel pressure should be maintained at a substantially constant value by suppressing variation in fuel pressure during the engine operation.
To secure increase of fuel pressure at starting and to suppress sequential fuel pressure variation, as shown in JP-U-5-1854, an accumulator is connected to a common rail (delivery pipe) for the fuel injection valve of each cylinder. A control valve and a high-pressure regulator for regulating fuel pressure is connected to the common rail, so that variation in fuel pressure during engine operation is suppressed by the high-pressure regulator. Further, during engine operation, the control valve is opened to introduce a part of the high-pressure fuel into the accumulator. At stopping of the engine, the control valve is closed to seal up high-pressure fuel in the accumulator. Subsequently at starting of the engine, the control valve is opened to introduce high-pressure fuel already in the accumulator into the common rail so that the rail fuel pressure is increased promptly at engine starting to improve starting performance.
However, in the above-described fuel supply apparatus, since the control valve, accumulator, and high-pressure regulator are necessary to secure improved starting performance while also suppressing sequential fuel pressure variation, the construction of the fuel supply system is complicated and contrary to desired requirements of small-sized apparatus and low cost.